Introduction to Fluid Mechanics Topic 1: Tutorial Questions

1. Faculty of Sciences
Department of Physical & Chemical Sciences
January—May 2021 Prof. Sello Alfred Likuku
Office Block 28
BSB 228: Introduction to Fluid Mechanics

2. March 13, 2021 2
1. Define internal, external, and open-channel flows.
2. Define incompressible flow and incompressible fluid.
3. Must the flow of a compressible fluid necessarily be treated as compressible?
4. What is the no-slip condition? What causes it?
5. What is forced flow? How does it differ from natural flow?
6. Is flow caused by winds forced or natural flow?
7. What is a boundary layer? What causes a boundary layer to develop?
8. What is the difference between the classical and the statistical approaches?
9. What is a steady-flow process?
10. Define stress, normal stress, shear stress, and pressure.
11. What are system, surroundings, and boundary?
12. When is a system a closed system, and when is it a control volume?
13. What is the difference between kg-mass and kg-force?
Problems 1–13 are concept questions, and you are encouraged to answer
them all
1-2 Tutorial Questions

3. March 13, 2021 3
14. A spherical balloon with a diameter of 6 m is filled with helium at 20°C and 200 kPa. Determine
the mole number and the mass of the helium in the balloon.. [9.28 kmol.; 37.2 kg]
15. Determine the mass and the weight of the air contained in a room whose dimensions are 6 m × 6
m×8 m. Assume the density of the air is 1.16 kg/m3. [334.08 kg; 3277 N, based on g = 9.81 m/s2]
16. At 45° latitude, the gravitational acceleration as a function of elevation z above sea level is given
by g = a – bz, where a = 9.81 m/s2 and b = 3.32×10–6 s–2. Determine the height above sea level
where the weight of an object will decrease by 1 percent. [29,548 m]
17. A 68-kg astronaut took his bathroom scale (a spring scale) and a beam scale (compares masses) to
the moon where the local gravity is g = 1.67 m/s2. Determine how much he will weigh (a) on the
spring scale and (b) on the beam scale. [(a) 113.43 N; (b) 667.23 N]
18. The acceleration of high-speed aircraft is sometimes expressed in g’s (in multiples of the standard
acceleration of gravity). Determine the net upward force, in N, that a 90-kg man would experience
in an aircraft whose acceleration is 6 g’s.
19. The value of the gravitational acceleration g decreases with elevation from 9.81 m/s2 at sea level to
9.77 m/s2 at an altitude of 13,000 m, where large passenger planes cruise. Determine the percent
reduction in the weight of an airplane cruising at 13,000 m relative to its weight at sea level.
20. A 5-kg rock is thrown upward with a force of 150 N at a location where the local gravitational
acceleration is 9.79 m/s2. Determine the acceleration of the rock, in m/s2.
1-2 Tutorial Questions